[QGIS Commit] r13997 - in docs/trunk/english_us/user_guide: .
plugins_georeferencer_images
svn_qgis at osgeo.org
svn_qgis at osgeo.org
Mon Aug 2 10:38:02 EDT 2010
Author: dassau
Date: 2010-08-02 14:38:01 +0000 (Mon, 02 Aug 2010)
New Revision: 13997
Added:
docs/trunk/english_us/user_guide/plugins_georeferencer_images/mActionGDALScript.png
docs/trunk/english_us/user_guide/plugins_georeferencer_images/mActionLinkGeorefToQGis.png
docs/trunk/english_us/user_guide/plugins_georeferencer_images/mActionLinkQGisToGeoref.png
docs/trunk/english_us/user_guide/plugins_georeferencer_images/mActionStartGeoref.png
docs/trunk/english_us/user_guide/plugins_georeferencer_images/transformation_settings.png
Modified:
docs/trunk/english_us/user_guide/plugins_georeferencer.tex
docs/trunk/english_us/user_guide/plugins_georeferencer_images/choose_points.png
docs/trunk/english_us/user_guide/plugins_georeferencer_images/georefplugin.png
Log:
update to georeferencer plugin
Modified: docs/trunk/english_us/user_guide/plugins_georeferencer.tex
===================================================================
--- docs/trunk/english_us/user_guide/plugins_georeferencer.tex 2010-08-02 09:00:59 UTC (rev 13996)
+++ docs/trunk/english_us/user_guide/plugins_georeferencer.tex 2010-08-02 14:38:01 UTC (rev 13997)
@@ -7,25 +7,73 @@
%\updatedisclaimer
The Georeferencer Plugin is a tool for generating world files for rasters.
-It allows you to reference rasters to geographic or projected coordinate systems by creating a
-world file, or by transforming the raster to a new coordinate system. The basic approach to georeferencing a raster is to locate points on the raster for which you can accurately determine their coordinates. The source of the coordinates can be:
+It allows you to reference rasters to geographic or projected coordinate
+systems by creating a new GeoTiff or by adding a world file to the
+existing image. The basic approach to georeferencing a raster is to locate
+points on the raster for which you can accurately determine their coordinates.
+\minisec{Features}
+
+\begin{table}[h]\index{Georeferencer!tools}
+\centering\small
+\renewcommand{\arraystretch}{2}
+ \begin{tabular}{|m{1cm}|m{5.4cm}|m{1cm}|m{5.4cm}|}
+ \hline \textbf{Icon} & \textbf{Purpose} & \textbf{Icon} &
+ \textbf{Purpose} \\
+ \hline \includegraphics[width=0.7cm]{mActionAddRasterLayer} & Open raster &
+ \includegraphics[width=0.7cm]{mActionStartGeoref} & Start georeferencing \\
+ \hline \includegraphics[width=0.7cm]{mActionGDALScript} & Generate GDAL script &
+ \includegraphics[width=0.7cm]{mActionFileOpen} & Load GCP Points \\
+ \hline \includegraphics[width=0.7cm]{mActionFileSave} & Save GCP Points as &
+ \includegraphics[width=0.7cm]{mActionOptions} & Transformation settings \\
+ \hline \includegraphics[width=0.7cm]{mActionCapturePoint} & Add Point &
+ \includegraphics[width=0.7cm]{mActionDeleteSelected} & Delete Point \\
+ \hline \includegraphics[width=0.7cm]{mActionEditPaste} & Move GCP Point &
+ \includegraphics[width=0.7cm]{mActionPan} & Pan \\
+ \hline \includegraphics[width=0.7cm]{mActionZoomIn} & Zoom in &
+ \includegraphics[width=0.7cm]{mActionZoomOut} & Zoom out \\
+ \hline \includegraphics[width=0.7cm]{mActionZoomToLayer} & Zoom to layer &
+ \includegraphics[width=0.7cm]{mActionZoomLast} & Zoom Last \\
+ \hline \includegraphics[width=0.7cm]{mActionZoomNext} & Zoom Next &
+ \includegraphics[width=0.7cm]{mActionLinkGeorefToQGis} & Link Georeferencer to QGIS \\
+ \hline \includegraphics[width=0.7cm]{mActionLinkQGisToGeoref} & Link QGIS to Georeferencer &
+ & \\
+\hline
+\end{tabular}
+\caption{Georeferencer Tools}\label{tab:georeferencer_tools}
+\end{table}
+
+\minisec{Usual procedure}
+
+As X and Y coordinates (DMS (dd mm ss.ss), DD (dd.dd) or projected coordinates
+(mmmm.mm) which correspond with the selected point on the image, two
+alternative procedures can be used:
+
\begin{enumerate}
-\item The raster itself, sometimes coordinates are literally `written' on the raster.
-In this case you can enter the coordinates manually.
-\item Other georeferenced data, this can be either vector or raster data that contain the same objects/features that you have on the raster that you want to georeference. In this case you can enter the coordinates by clicking on the reference dataset loaded in QGIS map canvas.
+\item The raster itself sometimes provides crosses with coordinates
+`written' on the image. In this case you can enter the coordinates manually.
+\item Using already georeferenced layers, this can be either vector or
+raster data that contain the same objects/features that you have on
+the image that you want to georeference and the projection you want to
+have your image. In this case you can enter the coordinates by
+clicking on the reference dataset loaded in QGIS map canvas.
\end{enumerate}
-The usual procedure for georeferencing an image involves selecting multiple points on the raster,
-specifying their coordinates, and choosing a relevant transformation type. Based on the input parameters and data, the plugin will compute the world file parameters. The more coordinates you provide, the better the result will be.
+The usual procedure for georeferencing an image involves selecting multiple
+points on the raster, specifying their coordinates, and choosing a relevant
+transformation type. Based on the input parameters and data, the plugin will
+compute the world file parameters. The more coordinates you provide, the
+better the result will be.
-The first step is to start QGIS and load the Georeferencer Plugin (see Section
-\ref{sec:load_core_plugin}) and click on the \toolbtntwo{georeferencer}{Georeferencer}
-icon which appears in the QGIS toolbar menu. The Georeferencer Plugin dialog appears as
-shown in Figure \ref{fig:georefplugin}.
+The first step is to start QGIS, load the Georeferencer Plugin (see Section
+\ref{sec:load_core_plugin}) and click on the
+\toolbtntwo{georeferencer}{Georeferencer} icon which appears in the
+QGIS toolbar menu. The Georeferencer Plugin dialog appears as shown
+in Figure \ref{fig:georefplugin}.
-For this example, we are using a topo sheet of South Dakota from SDGS. It can later be visualized
-together with the data from the GRASS spearfish60 location. You can download the topo sheet here:
+For this example, we are using a topo sheet of South Dakota from SDGS.
+It can later be visualized together with the data from the GRASS spearfish60
+location. You can download the topo sheet here:
\url{http://grass.osgeo.org/sampledata/spearfish\_toposheet.tar.gz}
\begin{figure}[ht]
@@ -37,15 +85,25 @@
\minisec{Entering ground control points (GCPs)}\label{georeferencer_entering}
\begin{enumerate}
-\item To start georeferencing an unreferenced raster, we must load it using the \browsebutton browse button. The raster will show up in the main working area of the dialog. Once the raster is loaded, we can start to enter reference points.
+\item To start georeferencing an unreferenced raster, we must load it using
+the \includegraphics[width=0.7cm]{mActionAddRasterLayer} button. The raster
+will show up in the main working area of the dialog. Once the raster is
+loaded, we can start to enter reference points.
+\item Using the \toolbtntwo{mActionCapturePoint}{Add Point} button, add
+points to the main working area and enter their coordinates
+(See Figure \ref{fig:choose_points}). For this procedure you have two
+options:
-\item Using the \toolbtntwo{mActionCapturePoint}{Add Point} button, add points to the main working area and enter their coordinates (See Figure \ref{fig:choose_points}). For this procedure you have two options:
-
\begin{enumerate}
-\item Click on a point in the raster map and enter the X and Y coordinates manually
-\item Click on a point in the raster map and choose the button \toolbtntwo{pencil}{from map canvas} to add the X and Y coordinates with the help of a georeferenced map already loaded in QGIS.
+\item Click on a point in the raster image and enter the X and Y coordinates manually
+\item Click on a point in the raster image and choose the button
+\toolbtntwo{pencil}{from map canvas} to add the X and Y coordinates with the help
+of a georeferenced map already loaded in the QGIS map canvas.
\end{enumerate}
-\item Continue entering points. You should have at least 4 points, and the more coordinates you can provide, the better the result will be. There are additional tools on the plugin dialog to zoom and pan the working area in order to locate a relevant set of GCP points.
+\item Continue entering points. You should have at least 4 points, and the
+more coordinates you can provide, the better the result will be. There are
+additional tools on the plugin dialog to zoom and pan the working area in
+order to locate a relevant set of GCP points.
\end{enumerate}
\begin{figure}[ht]
@@ -54,44 +112,108 @@
\caption{Add points to the raster image \nixcaption}\label{fig:choose_points}
\end{figure}
-The points that are added to the map will be stored in a separate text file ([filename].points) which is stored together with the raster image. This allows us to reopen the Georeferencer plugin at a later date and add new points or delete existing ones to optimize the result. The points file contains values of the form: mapX, mapY, pixelX, pixelY. You can also \button{Load GCPs} and \button{Save GCPs} to different directories if you like.
+The points that are added to the map will be stored in a separate text
+file ([filename].points) usually together with the raster image.
+This allows us to reopen the Georeferencer plugin at a later date and add
+new points or delete existing ones to optimize the result. The points file
+contains values of the form: mapX, mapY, pixelX, pixelY. You can use the
+\includegraphics[width=0.7cm]{mActionFileOpen} 'Load GCP Points' and
+\includegraphics[width=0.7cm]{mActionFileSave} 'Save GCP Points' buttons to
+manage the files.
-\minisec{Choosing the transformation}\label{georeferencer_transformation}
+\minisec{Defining the transformation settings}\label{georeferencer_transformation}
-After you have added your GCPs to the raster image, you need to select the transformation type for the georeferencing process. Depending on how many ground control point you have captured, you may want to use different transformation algorithms. Choice of transformation algorithm is also dependent on the type and quality of input data and the amount of geometric distortion that you are willing to introduce to final result.
+After you have added your GCPs to the raster image, you need to define the
+transformation settings for the georeferencing process.
-Currently, several algorithms are available:
+\begin{figure}[ht]
+\centering
+ \includegraphics[clip=true,width=8cm]{transformation_settings}
+ \caption{Defining the georeferencer transformation settings \nixcaption}\label{fig:georef_transform}
+\end{figure}
-\begin{enumerate}
-\item Linear
-\item Helmert
-\item Polynomial 1
-\item Polynomial 2
-\item Polynomial 3
-\item Thin plate spline (TPS)
-\end{enumerate}
+\minisec{Available Transformation algorithms}
+Depending on how many ground control point you have captured, you may want
+to use different transformation algorithms. Choice of transformation
+algorithm is also dependent on the type and quality of input data and
+the amount of geometric distortion that you are willing to introduce
+to final result.
+
+Currently, following algorithms are available:
+
\begin{itemize}[label=--]
-\item The Linear algorithm is used to create a world-file, and is different from the other algorithms, as it does not actually transform the raster. This algorithm likely won't be sufficient if you are dealing with scanned material.
-\item The Helmert transformation performs simple scaling and rotation transformations.
-\item The Polynomial algorithms are among the most widely used algorithms for georeferencing, and each one differs by the degree of distortion introduced to match source and destination ground control points. The most widely used polynomial algorithm is the second order polynomial transformation, which allows some curvature. First order polynomial transformation (affine) preserves colliniarity and allows scaling, translation and rotation only.
-\item The Thin plate spline (TPS) algorithm is a more modern georeferencing method, which is able to introduce local deformations in the data. This algorithm is useful when very low quality originals are being georeferenced.
+\item The \textbf{Linear algorithm} is used to create a world-file, and is different
+from the other algorithms, as it does not actually transform the raster.
+This algorithm likely won't be sufficient if you are dealing with scanned
+material.
+\item The \textbf{Helmert transformation} performs simple scaling and rotation
+transformations.
+\item The \textbf{Polynomial algorithms} 1-3 are among the most widely
+used algorithms
+for georeferencing, and each one differs by the degree of distortion
+introduced to match source and destination ground control points. The
+most widely used polynomial algorithm is the second order polynomial
+transformation, which allows some curvature. First order polynomial
+transformation (affine) preserves colliniarity and allows scaling,
+translation and rotation only.
+\item The \textbf{Thin plate spline (TPS) algorithm} is a more
+modern georeferencing method, which is able to introduce local
+deformations in the data. This algorithm is useful when very low
+quality originals are being georeferenced.
\end{itemize}
-\minisec{Running the transformation}\label{georeferencer_running}
+\minisec{Define the Resampling method}
-\begin{enumerate}
-\item When the GCPs have been collected, and the transformation has been chosen, press either \button{Create} to create a new raster or \button{Create and load layer} to automatically add the new raster to the layer list.
-\item A warning message will appear that will inform you that a new raster (in GeoTIFF format) will be created.
-\item After hitting OK, you will also be asked to choose a resampling method. There are three methods available:
-\end{enumerate}
+The type of resampling you choose will likely depending on your input data
+and the ultimate objective of the exercise. If you don't want to change
+statistics of the image, you might want to choose Nearest neighbour,
+whereas a Cubic resampling will likely provide a more smoothed result.
+It is prossible to choose between five different resampling methods.
+
\begin{enumerate}
\item Nearest neighbour
\item Linear
\item Cubic
+\item Cubic Spline
+\item Lanczos
\end{enumerate}
-\begin{Tip}\caption{\textsc{Choosing the resampling method}}
-The type of resampling you choose will likely depending on your input data and the ultimate objective of the exercise. If you don't want to change statistics of the image, you might want to choose Nearest neighbour, whereas a Cubic resampling will likely provide a more smoothed result.
-\end{Tip}
+\minisec{Define the Output raster}
+
+There are several options that need to be defined for the georeferenced output
+raster.
+
+\begin{itemize}[label=--]
+\item The checkbox \checkbox{Create world file} is only available, if
+you decide to use the linear transformation type, because this means that
+the raster image actually won't be transformed. In this case, the field
+Output raster is not activated, because only a new world-file will be
+created.
+\item For all other transformation type you have to define an \textbf{Output
+raster}. As default a new file ([filename]\_modified) will be created in
+the same folder together with the original raster image.
+\item As a next step you have to define the \textbf{Target SRS}
+(Spatial Reference System) for the georeferenced raster
+(see section \ref{label_projections}).
+\item If you like, you can also \textbf{generate a pdf report}. It includes
+information about the used transformation parameters. An image of the
+residuals and a list with all GCPs and their RMS errors.
+\item Furthermore you can activate the \checkbox{Set Target Resolution}
+checkbox and define pixel resolution of the output raster. Default horizontal
+and vertical resolution is 1,
+\item The \checkbox{Use 0 for transparency when needed} can be activated, if
+pixels with the value 0 shall be visualized transparent. In our example
+toposheet all white areas would be transparent.
+\item Finally \checkbox{Load in QGIS when done} loads the output raster
+automatically into the QGIS map canvas when the transformation is done.
+\end{itemize}
+
+\minisec{Running the transformation}\label{georeferencer_running}
+
+After all GCPs have been collected and all transformation settings are
+defined, just press the button \includegraphics[width=0.7cm]{mActionStartGeoref}
+'Start georeferencing' to create the new georeferenced raster.
+
+
Modified: docs/trunk/english_us/user_guide/plugins_georeferencer_images/choose_points.png
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Modified: docs/trunk/english_us/user_guide/plugins_georeferencer_images/georefplugin.png
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